Friction seals are used in wellbores, such as oil and gas wells. These seals are used in situations in which the annulus between two essentially coaxial tubular members, such as a casing and a drill string, must be split into an uphole zone and a downhole zone which are in fluid isolation from each other.
Such seals, like that disclosed in U.S. Pat. No. 5,333,692 to Baugh, et al., may comprise a circular sealing ring which is mechanically mounted to the outer circumference of the inner tubular member. In the run-in position, this sealing ring and its mount are held in relatively close proximity to the inner tubular member, so that the inner tubular member and the seal may freely transit downhole into the proper setting position. Once in the setting position, the sealing ring must be forced outward into secure contact with the inner surface of the outer tubular member.
This sealing action is usually accomplished by actuating a setting device, such as a wedge-shaped ring, and using the setting device to force the sealing ring outward, deforming its mechanical mounting to the inner tubular member as necessary. Once sufficient force is applied, the sealing ring is forced into a tight surface-to-surface sealing arrangement between the outer surface of the sealing ring and the inner surface of the outer tubular member.
In the annulus between the inner and outer tubular members, the seal thus creates an uphole zone and a downhole zone which are in fluid isolation from each other. Leakage around the inner surface of the sealing ring is generally prevented by the presence of the wedge or other setting device which was used to force the sealing ring outward.
However, these sealing arrangements are not entirely reliable. Excess hydraulic pressure in the annulus between the two tubular members can cause the seal to slip in one direction or the other, pushing the seal out of the desired position. This situation may also cause deformation of the sealing surface with resultant leakage.
Accordingly, it is desirable to provide a sealing apparatus which utilizes any unbalanced or excess up-hole or down-hole hydraulic pressure to enhance the sealing force and to reinforce the strength of the seal.
It is an object of the invention to provide a seal for use in a wellbore which, once set, is reinforced by hydraulic pressure exerted against the sealing device from either an up-hole or a down-hole direction.